#!/usr/bin/perl -w

use strict;
use Mail::Sender;

# How these are defined is left as an exercise to the reader
my ($from, $to, $subject, $message, $file, $server);

# Create our message handler
ref (my $mail = new Mail::Sender { smtp => $server } ) or die "Mail er
+ror: $Mail::Sender::Error\n";

# Message header
$mail->Open({ from => $from, to => $to, subject => $subject }) or die 
+"Mail error: $Mail::Sender::Error\n";

$mail->Body;

# Add the "intro" message
$mail->SendLineEnc("$message\n");

# Attachment
$mail->Attach({ description => 'My Attachment', 
               ctype => 'text/plain', 
               encoding => '7bit', 
               disposition => 'attachment; filename="attach.txt"; type
+="Text file"', 
               file => 'attach.txt' } );

# Close & send message

$mail->Close;
[download]

Nope, Net::SMTP is probably a more existing choice :)

SMTP is not responsible for your MIME-problems, so Net::SMTP has little to do with the actual attachment creation. MIME::Lite is probably the easiest way to create correct messages, which can then be sent using Net::SMTP of course.